Polyaxial locking mechanism

ABSTRACT

A bone plate system comprises a bone plate including a first surface and a second surface, the bone plate including at least one threaded aperture, the threaded aperture being tapered between the first surface and the second surface. The bone plate system further comprises at least one fastener including an elongate shaft and a threaded head, the threaded head being tapered between a proximal end of the threaded head and a distal end of the threaded head, wherein a plurality of circumferentially spaced recesses are formed in the threaded head and define a plurality of threaded tabs. The at least one fastener is configured for insertion within the at least one threaded aperture at a plurality of different insertion angles while achieving a locking engagement between the threaded head and the threaded aperture.

This application is a continuation of U.S. patent application Ser. No.14/025,267, entitled “POLYAXIAL LOCKING MECHANISM”, and filed on Sep.12, 2013, which claims the benefit of U.S. Provisional PatentApplication Ser. No. 61/865,247, entitled “POLYAXIAL LOCKING MECHANISM”,and filed on Aug. 13, 2013, the benefit of priority of each of which areclaimed hereby, and are incorporated by reference herein in itsentirety.

BACKGROUND

The present patent application relates to locking mechanisms, and, moreparticularly, to polyaxial locking mechanisms for surgical componentssuch as bone plates.

In certain orthopedic surgical procedures, it is necessary to securemultiple bones or bone portions relative to each other. For example, inwrist or ankle surgeries, the joining of two or more bone portions orfragments may be required to promote healing and restore function. Theneed for such procedures may be the result of physical trauma fromfractures or dislocations, degenerative diseases, or the like.

Various types of bone plate systems can be used for internal fixation ofbones. Exemplary bone plate systems can include a bone plate that isconfigured to be attached to one or more bone portions spanning afracture line. The bone plate generally includes a plurality ofapertures through which bone screws and/or bone pegs are inserted forengaging the bone. In an example, the bone plate systems can includelocking screws, which can be adapted for locking in corresponding plateapertures in a fixed orientation. An advantage of “locked plating”systems is that they do not require the bone plate to be compressed tothe bone. Rather, the interface formed between the bone plate and thelocking screws can eliminate the need for compression between the plateand the bone. In another example, the bone plate systems can includenon-locking screws, which can be configured for insertion at anorientation selected by the user. Unlike “locked plating” systems,“non-locked plating” systems rely on the friction formed between thebone plate and the bone when the screw is inserted through the boneplate and tightened.

Although numerous bone plate systems exist for use in orthopedicsurgical procedures, there is still a need for improved bone platesystems that provide the locking characteristics associated withtraditional locking screws as well as the variable screw orientationassociated with traditional non-locking screws.

OVERVIEW

To better illustrate the cleaning system disclosed herein, anon-limiting list of examples is provided here:

In Example 1, a bone plate system can be provided that includes a boneplate having a first surface and a second surface, the bone plateincluding at least one threaded aperture, the threaded aperture beingtapered between the first surface and the second surface. The bone platesystem further includes at least one fastener including an elongateshaft and a threaded head, the threaded head being tapered between aproximal end of the threaded head and a distal end of the threaded head,wherein a plurality of circumferentially spaced recesses are formed inthe threaded head and define a plurality of threaded tabs. The at leastone fastener is configured for insertion within the at least onethreaded aperture at a plurality of different insertion angles whileachieving a locking engagement between the threaded head and thethreaded aperture.

In Example 2, the bone plate system of Example 1 is optionallyconfigured such that a first taper angle is formed between alongitudinal axis of the threaded aperture and an internally threadedsurface of the threaded aperture, and a second taper angle is formedbetween a longitudinal axis of the threaded head and an externallythreaded surface of the threaded head, wherein the first taper angle isgreater than the second taper angle.

In Example 3, the bone plate system of Example 2 is optionallyconfigured such that the first taper angle is between about 10 degreesand about 20 degrees, and the second taper angle is between about 5degrees and about 15 degrees.

In Example 4, the bone plate system of any one of or any combination ofExamples 2-3 is configured such that the plurality of recesses extendfrom the proximal end to the distal end of the threaded head in adirection that is substantially parallel to the longitudinal axis of thethreaded head.

In Example 5, the bone plate system of any one of or any combination ofExamples 2-4 is optionally configured such that the internally threadedsurface of the threaded aperture includes double lead threads.

In Example 6, the bone plate system of any one of or any combination ofExamples 1-5 is optionally configured such that the threaded apertureincludes internal threads defining a first pitch, and the threaded headincludes external threads defining a second pitch.

In Example 7, the bone plate system of Example 6 is optionallyconfigured such that the first pitch and the second pitch are the same.

In Example 8, the bone plate system of Example 6 is optionallyconfigured such that the first pitch and the second pitch are different.

In Example 9, the bone plate system of any one of or any combination ofExamples 1-8 is optionally configured to include three or more recessesin the threaded head.

In Example 10, the bone plate system of any one of or any combination ofExamples 1-9 is optionally configured such that a circumference of thethreaded head includes a threaded circumference portion defined by thethreaded tabs and a non-threaded circumference portion defined by therecesses, wherein the threaded circumference portion is greater than thenon-threaded circumference portion.

In Example 11, the bone plate system of any one of or any combination ofExamples 1-10 is optionally configured such that the threaded head is atleast partially formed from a first material that is softer than asecond material of the bone plate such that the threaded head can deformduring insertion within the threaded aperture of the bone plate.

In Example 12, a bone plate system can be provided that includes a boneplate including at least one tapered aperture having a longitudinal axisand a threaded internal surface, the tapered aperture defining a firsttaper angle between the longitudinal axis of the tapered aperture andthe threaded internal surface. The bone plate system further includes atleast one fastener including an elongate shaft and a tapered head havinga threaded external surface and a longitudinal axis, the tapered headdefining a second taper angle between the longitudinal axis of thetapered head and the threaded external surface, wherein a plurality ofcircumferentially spaced recesses are formed in the tapered head anddefine interruptions in the threaded external surface of the taperedhead. The first taper angle of the tapered aperture is greater than thesecond taper angle of the tapered head such that the at least onefastener can be inserted within the at least one tapered aperture at aplurality of different insertion angles.

In Example 13, the bone plate system of Example 12 is optionallyconfigured such that the first taper angle is between about 10 degreesand about 20 degrees, and the second taper angle is between about 5degrees and about 15 degrees.

In Example 14, the bone plate system of any one of or any combination ofExamples 12-13 is optionally configured such that the interruptions inthe threaded external surface of the tapered head define a plurality ofthreaded tabs on the tapered head.

In Example 15, the bone plate system of Example 14 is optionallyconfigured such that a circumferential surface area defined by thethreaded tabs is greater than a circumferential surface area defined bythe recesses in the tapered head.

In Example 16, the bone plate system of any one of or any combination ofExamples 12-15 is optionally configured such that the threaded internalsurface of the tapered aperture includes threads defining a first pitchand the threaded external surface of the tapered head includes threadsdefining a second pitch, wherein the first pitch and the second pitchare the same.

In Example 17, the bone plate system of any one of or any combination ofExamples 12-15 is optionally configured such that the threaded internalsurface of the tapered aperture includes threads defining a first pitchand the threaded external surface of the tapered head includes threadsdefining a second pitch, wherein the first pitch and the second pitchare different.

In Example 18, a polyaxial locking mechanism can be provided thatincludes at least one tapered aperture formed in a component, whereinthe tapered aperture includes an internally threaded surface. Thepolyaxial locking mechanism further includes at least one fastenerconfigured for insertion within the at least one tapered aperture at aplurality of different insertion angles, the at least one fastenerincluding an elongate shaft and a tapered head, wherein a plurality ofcircumferentially spaced recesses are formed in the tapered head anddefine a plurality of threaded tabs. The tapered head includes athreaded surface area portion defined by the threaded tabs and anon-threaded surface area portion defined by the recesses, wherein thethreaded surface area portion is greater than the non-threaded surfacearea portion.

In Example 19, the polyaxial locking mechanism of Example 18 isoptionally configured such that the internally threaded surface of thetapered aperture includes double lead threads.

In Example 20, the polyaxial locking mechanism of any one of or anycombination of Examples 18-19 is optionally configured such that thetapered head is at least partially formed from a first material that issofter than a second material of the component such that the taperedhead can deform dining insertion within the tapered aperture of thecomponent.

In Example 21, the bone plate system or polyaxial locking mechanism ofany one of or any combination of Examples 1-20 is optionally configuredsuch that all elements or options recited are available to use or selectfrom.

This overview is intended to provide an overview of subject matter ofthe present patent application. It is not intended to provide anexclusive or exhaustive explanation of the invention. The detaileddescription is included to provide further information about the presentpatent application.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, which are not necessarily drawn to scale, like numeralsmay describe similar components in different views. Like numerals havingdifferent letter suffixes may represent different instances of similarcomponents. The drawings illustrate generally, by way of example, butnot by way of limitation, various embodiments discussed in the presentdocument.

FIGS. 1A and 1B are perspective and side views, respectively, of a boneplate system in accordance with at least one example of the presentdisclosure.

FIGS. 2A and 2B are cross-sections of the perspective and side views ofFIGS. 1A and 1B, respectively, in accordance with at least one exampleof the present disclosure.

FIG. 3 is a top view of the bone plate system in accordance with atleast one example of the present disclosure.

FIG. 4 is a cross-sectional view of a threaded aperture of the boneplate system in accordance with at least one example of the presentdisclosure.

FIG. 5 is an enlarged cross-sectional view of a portion of the threadedaperture of FIG. 4.

FIG. 6 is a side view of a locking fastener in accordance with at leastone example of the present disclosure.

FIG. 7 is a proximal end view of the locking fastener in accordance withat least one example of the present disclosure.

FIG. 8 is a cross-sectional view of a portion of the locking fastener inaccordance with at least one example of the present disclosure.

FIG. 9 depicts the locking fastener at an on-axis insertion angle of 0degrees in accordance with at least one example of the presentdisclosure.

FIG. 10 depicts the locking fastener inserted at an off-axis, non-zeroinsertion angle in accordance with at least one example of the presentdisclosure.

DETAILED DESCRIPTION

The present patent application generally relates to bone plate systemshaving a polyaxial locking relationship between at least one fastenerand at least one aperture in a bone plate. The bone plate system caninclude any type of bone plate configured for attachment to one or morebones, bone portions, or bone fragments, such as bones of a patient'sextremities. In certain examples, the bone plate can be configured forattachment to a hand, a wrist, a foot, an ankle, or a spine. The atleast one fastener of the bone plate system can be configured forinsertion in the at least one aperture in a plurality of differentinsertion angles defining a plurality of different axes, i.e., the atleast one fastener can be “polyaxial.” An externally threaded headsurface of the at least one fastener can be configured to engage aninternally threaded aperture surface of the at least one aperture toprovide a locking engagement between the at least one fastener and thebone plate. An advantage of such “locked plating” systems can be thatthey do not require the bone plate to be compressed to the bone uponimplantation due to the interface formed between the bone plate and thehead of the fastener.

For purposes of example only, the bone plate system of the presentdisclosure is described with reference to a fastener in the form of abone screw having a threaded head and a threaded shaft. However,numerous other types of fasteners can be used in place of or in additionto a bone screw, such as a bone peg having a threaded head and anon-threaded shaft. Thus, bone screws are described merely for purposesof example and not limitation, and the scope of the present disclosurecovers any fastener that allows for polyaxial insertion and lockingengagement with a bone plate.

FIGS. 1A and 1B are perspective and side views, respectively, of a boneplate system 10 in accordance with at least one example of the presentdisclosure. As illustrated in FIG. 1, the bone plate system 10 caninclude a bone plate 12 having a proximal end 14, a distal end 16, astem portion 18, and a head portion 20. With reference to FIG. 1B, thebone plate 12 can include a bone contacting first surface 22 configuredfor placement against one or more bones in a patient's body, and asecond surface 24 generally opposing the first surface 22.

At least one of the stem portion 18 and the head portion 20 can includeone or more internally threaded apertures 26 extending between the firstsurface 22 and the second surface 24 of the bone plate 12 and configuredto receive a locking fastener (e.g., a fastener with a threaded head),as will be discussed in further detail below. FIG. 1A depicts twothreaded apertures 26 in the stem portion 18 and six threaded apertures26 in the head portion 20 merely for purposes of example and notlimitation. Thus, bone plates having one or more threaded apertures arecontemplated and within the scope of the present disclosure. Althoughnot shown in FIGS. 1A and 1B, the bone plate 12 can include one or morenon-threaded apertures configured to receive a non-locking fastener(e.g., a fastener with a non-threaded head). Furthermore, the threadedapertures 26 can also receive non-locking fasteners.

In various examples, the bone plate 12 can also include one or moreelongated slots 28 and one or more K-wire holes 30. In an example,during initial fixation and placement of the bone plate 12, eachelongated slot 28 can be configured to receive a fastener. The fastenercan be loosely tightened in place on the bone to allow for longitudinaladjustment of the bone plate 12 to the final, desired position. Once thedesired position has been achieved, the fastener can be furthertightened within the elongated slot 28. In an example, the K-wire holes30 can be configured for insertion of K-wires at various angles in orderto temporarily fix the bone plate 12 to the underlying bone or to targetbone fragments. The K-wires can be removed from the K-wire holes 30after the bone plate 12 is secured to the bone, such as after insertingfastener into one or more of the internally threaded apertures 26.

As further illustrated in FIGS. 1A and 1B, the threaded apertures 26 canbe configured to receive a locking fastener 32 (only one being shown).The locking fastener 32 can include an externally threaded head 34configured to engage the internally threaded aperture 26. As will bediscussed in further detail below, the locking fastener 32 can beinserted into the threaded aperture 26 in a plurality of differentinsertion angles while achieving a locking engagement between thethreaded head 34 and the threaded aperture 26. The locking fastener 32can further include an elongate shaft 36 configured for insertion withina bone underlying the plate 12. In an example, the elongate shaft 36 caninclude one or more external threads 38, as shown in FIGS. 1A and 1B.This type of locking fastener can be generally referred to as a “lockingscrew.” In other examples, the elongate shaft 36 can include asubstantially smooth outer surface (i.e., no external threads). Thistype of locking fastener can be generally referred to as a “lockingpeg.”

FIGS. 2A and 2B are cross-sections of the perspective and side views ofFIGS. 1A and 1B, respectively, in accordance with at least one exampleof the present disclosure. As illustrated in FIGS. 2A and 2B, each ofthe threaded apertures 26 can define a longitudinal axis 40 extendingthrough the threaded aperture 26 between the first surface 22 and thesecond surface 24 of the bone plate 12. The longitudinal axis 40 canrepresent the “centerline” of the threaded aperture 26 and is thereforedependent on the orientation in which the threaded aperture 26 is formedin the bone plate 12. In various examples, the threaded aperture 26 canbe formed in the bone plate 12 such that it extends generallyperpendicular to the first surface 22 and the second surface 24, or thethreaded aperture 26 can be formed in the bone plate 12 such that itextends at a non perpendicular angle relative to the first surface 22and the second surface 24. Regardless of the orientation of the threadedaperture 26, the longitudinal axis 40 defines only one of the axes alongwhich the locking fastener 32 can be inserted. Thus, the threadedaperture 26 and the locking fastener 32 can define a “polyaxial”fastening system wherein the locking fastener 32 can be inserted intothe threaded aperture 26 in a plurality of different insertion anglesrelative to the longitudinal axis 40 of the aperture while achieving alocking engagement between the thread head 34 and the threaded aperture26. An example of this polyaxial locking capability is illustrated inFIGS. 2A and 2B, wherein the elongate shaft 36 of the locking fastener32 does not extend along the longitudinal axis 40 of the correspondingthreaded aperture 26, but instead forms an angle with the longitudinalaxis 40 while maintaining a locking connection between the externallythreaded head 34 and the internally threaded aperture 26.

FIG. 3 is a top view of the bone plate system 10 in accordance with atleast one example of the present disclosure further illustrating thelongitudinal axes 40 of the threaded apertures 26 of FIGS. 2A and 2B. Asshown in FIG. 3, the threaded apertures 26 can be oriented in differentdirections along the bone plate 12. In an example, the orientations ofthe threaded apertures 26 can represent common or “default” orientationsthat have been found to result in secure attachment of the bone plate 12to the underlying bones and/or bone fragments. Thus, a surgeon canchoose to insert the locking fastener 32 along the longitudinal axis 40of a selected aperture 26 and achieve a locking engagement between theexternally threaded head 34 of the locking fastener 32 and theinternally threaded aperture 26. However, if the “default” orientationis not desirable for one or more reasons, then the surgeon can choose toutilize the polyaxial capabilities of bone plate system 10 and insertthe locking fastener 32 into the threaded aperture 26 at an off-axisinsertion angle. The structure of the threaded apertures 26 and thelocking fasteners 32 that allows for such polyaxial locking capabilitieswill be further described with reference to FIGS. 4-10.

FIG. 4 is a cross-sectional view of one of the threaded apertures 26 inthe bone plate 12 taken along line 4-4 of FIG. 3. As illustrated in FIG.4, the threaded aperture 26 can include an internally threaded surface46 comprising one or more helical threads. The internally threadedsurface 46 can include any thread pitch suitable for mating with theexternally threaded head 34 of the locking fastener 32. In an example,the thread pitch can be between about 0.02 inches and about 0.06 inches,such as about 0.039 inches.

As further illustrated in FIG. 4, the threaded aperture 26 can be atapered aperture, such as a conical tapered aperture. The threadedaperture 26 can have a first opening 48 having a first internal diameterID1 and a second opening 50 having a second internal diameter ID2 thatis larger than the first internal diameter ID1. In an example, the firstinternal diameter ID1 can be about 0.130 inches and the second internaldiameter ID2 can be about 0.170 inches. A taper angle A can be definedbetween the longitudinal axis 40 and the internally threaded surface 46of the threaded aperture 26. Although any suitable taper angle A can beused, suitable taper angles A can be between about 5 degrees and about25 degrees, and more particularly between about degrees and about 20degrees, such as about 14 degrees.

With further reference to FIG. 4, the threaded aperture 26 can include arecess or counterbore in one or more of the first surface 22 and thesecond surface 24. For example, the bone plate 12 of FIG. 4 includes acounterbore 52 in the first surface 22. However, the counterbore 52could alternatively be formed in the second surface 24, or a pair ofcounterbores 52 could be formed in the first surface 22 and the secondsurface 24. The one or more counterbores 52 can be configured to improverepeatability of polyaxial locking performance and allow the threadedaperture 26 to be more easily inspected after manufacture.

FIG. 5 is an enlarged cross-sectional view of a portion of the threadedaperture 26 of FIG. 4. In various examples within the scope of thepresent disclosure, the internally threaded surface 46 of the threadedaperture 26 can define a single lead or multiple leads. The threadedaperture 26 of FIGS. 4 and 5 illustrates a double lead with start pointsspaced apart by about 180 degrees.

The internally threaded surface 46 can include V-shaped threads defininga series of roots 60 and crests 62 and having an internal thread angleT1. The thread angle T1 can be selected such that it is consistent withcommercially available tooling, such as 60 degrees (UN threads) or 29degrees (ACME threads). However, various other non-standard threadangles can be used. In the present example of the bone plate 12, theinternal thread angle T1 is about 60 degrees. A thread height H1 of thethreads of the internally threaded surface 46 can be defined between oneof the roots 60 and an adjacent one of the crests 62. As illustrated inFIG. 5, the roots 60 and/or the crests 62 can be truncated to avoid theformation of a “sharp” V-shape. A perfectly sharp 60 degree V-threadgenerally includes a thread height equal to about 0.866 of the pitch.However, with truncated threads, the thread height decreases. In anexample, the thread height H1 can be between about 0.008 inches andabout 0.015 inches, such as about 0.0118 inches.

FIG. 6 is a side view of the locking fastener 32 in accordance with atleast one example of the present disclosure. As illustrated in FIG. 6,the threaded head 34 of the locking fastener 32 can include anexternally threaded surface 70 comprising one or more helical threads.The externally threaded surface 70 can include any thread pitch suitablefor mating with the internally threaded surface 46 of the threadedaperture 26. In an example, the thread pitch may be between about 0.02inches and about 0.06 inches, such as about 0.039 inches. The threadpitch of the externally threaded surface 70 of the threaded head 34 canbe substantially identical to the thread pitch of the internallythreaded surface 46 of the threaded aperture 26. However, the threadpitch between the threaded head 34 of the locking fastener 32 and thethreaded aperture 26 of the bone plate 12 can be varied such that thereis a mismatch between thread pitches. In an example, a mismatch betweenthread pitches can increase the locking strength by increasing thecontact area on the flanks of the threads in the externally threadedsurface 70.

In various examples within the scope of the present disclosure, theexternally threaded surface 70 of the threaded head 34 can define asingle lead or multiple leads. Similar to the threaded aperture 26 ofFIGS. 4 and 5, the threaded head 34 of FIG. 6 illustrates a double leadwith start points spaced apart by about 180 degrees.

The threaded head 34 can include a proximal end 72 and a distal end 74.A non-threaded transition region 76 can be provided between the threadedhead 34 and the elongate shaft 36 adjacent to the distal end 74 of thethreaded head 34. As further illustrated in FIG. 6, the threaded head 34can include one or more recesses 78 circumferentially spaced around thethreaded head 34 and defining a plurality of threaded tabs 80. In anexample, the one or more recesses 78 can be formed by creatingtangential cuts in the externally threaded surface 70 of the threadedhead 34. The tangential cuts can have a depth sufficient to completelyremove the threads in the area of the recess 78 such that asubstantially smooth recessed surface is created. Alternatively, therecess 78 can be formed to a depth that retains the threads in the areaof the recess 78, albeit at a reduced height (between a root and a crestof the thread).

Each of the one or more recesses 78 can extend in a direction 81 atleast partially between the proximal end 72 and the distal end 74 of thethreaded head 34 that can be substantially parallel to a longitudinalaxis 82 of the locking fastener 32. The longitudinal axis 82 can extendthrough a center of the threaded head 34 and a center of the elongateshaft 36. Thus, the longitudinal axis 82 can alternatively be defined asthe longitudinal axis of the threaded head 34 or the longitudinal axisof the elongate shaft 36. In other examples, at least one of the one ormore recesses 78 can extend in a direction 81 between the proximal end72 and the distal end 74 of the threaded head 34 that forms a non-zeroangle with, and is therefore not parallel to, the longitudinal axis 82of the locking fastener 32. Thus, the one or more recesses 78 can extendin a direction that forms a non-perpendicular angle with a plane definedalong the proximal end 72 of the threaded head 34 and a plane definedalong the distal end 74 of the threaded head 34 (i.e., a “slanted”recess).

With further reference to FIG. 6, a distal end 84 of the elongate shaft36 can include a self-tapping tip 86 comprising one or more flutes. Theself-tapping tip 86 can provide the locking fastener 32 with the abilityto advance in a longitudinal direction when being turned, while at thesame time creating its own thread in the bone. In other examples, theelongate shaft 36 does not include a self-tapping tip 86, and the bonecan be pre-chilled prior to insertion of the locking fastener 32.

The one or more external threads 38 on the elongate shaft 36 can havethe same pitch and the same lead as the externally threaded surface 70of the threaded head 34. In other examples, the one or more externalthreads 38 can have a pitch and/or a lead that is different than theexternally threaded surface 70, such as a double lead on the threadedhead 34 and a single lead on the elongate shaft 36.

FIG. 7 is a proximal end view of the locking fastener 32 of FIG. 6 inaccordance with at least one example of the present disclosure. Asillustrated in FIG. 7, the threaded head 34 of the locking fastener 32can include a drive interface 90, such as a female drive interfaceconfigured to mate with a male drive interface on a driver device. In anexample, as shown in FIG. 7, the drive interface 90 can be a hexalobedrive interface. However, any suitable drive interface 90 can be usedincluding, but not limited to, a hex drive interface, a double hex driveinterface, a pentagon drive interface, a square drive interface, aslotted drive interface, a cross-recess drive interface, a Phillipsdrive interface, a Frearson drive interface, a Mortorq drive interface,a Pozidriv drive interface, a Supadriv drive interface, aPhillips/square drive interface, a pentalobe drive interface, apolydrive interface, or a spline drive interface.

As discussed above, the threaded head 34 of the locking fastener 32 caninclude one or more recesses 78. In the example illustrated in FIG. 7,the threaded head 34 includes three recesses 78 spaced circumferentiallyaround a perimeter of the threaded head 34 by an angle R of about 120degrees. In various examples, a larger or smaller number of recesses 78can be included, such as between 2 recesses and 5 recesses. The angularspacing can be, but is not necessarily, equal between adjacent recesses78. Thus, in an example, the angle R defined between adjacent recesses78 can be determined from the equation (R=360 degrees/X), where X is thetotal number of recesses in the threaded head 34. However, the recesses78 can be non-uniformly spaced such that at least one of the angles Rhas a value different than at least one of the other angles R.

As illustrated in FIG. 7, a circumference of the threaded head 34 can bedivided into a plurality of threaded circumference portions 92A and aplurality of non-threaded circumference portions 92B (or circumferenceportions having a reduced thread height as discussed above).Particularly, the non-threaded circumference portions 92B can be definedby the portions of the externally threaded surface 70 that have beenremoved by the recesses 78, and the threaded circumference portions 92Acan be defined by the remaining portions of the externally threadedsurface 70. Thus, the threaded circumference portions 92A and thenon-threaded circumference portions 92B can be viewed in terms of thecircumferential widths of these portions around the threaded head 34 (ina plane perpendicular to the longitudinal axis 82 of the lockingfastener 32), or in terms of the circumferential surface areas of theseportions determined by factoring in the circumferential widths and thelengths of the portions between the proximal end 72 of the threaded head34 and the distal end 74 of the threaded head 34 (see FIG. 6).Regardless of whether the threaded circumference portions 92A and thenon-threaded circumference portions 92B are viewed as circumferentialwidths or circumferential surface areas, in an example, the removed“circumference” of the recesses 78 can be less than the remaining“circumference” of the tabs 80 as depicted in FIGS. 6 and 7. In otherexamples, however, the removed “circumference” of the recesses 78 can beequal to or greater than the remaining “circumference” of the tabs 80.

FIG. 8 is a cross-sectional view of a portion of the locking fastener 32taken along line 8-8 of FIG. 6. As illustrated in FIG. 8, the threadedhead 34 can be a tapered head, such as a conical tapered head. Thethreaded head 34 can have a first external diameter ED1 at the distalend 74 and a second external diameter ED2 at the proximal end 72 that islarger than the first external diameter ED1. In an example, the firstexternal diameter ED1 can be about 0.132 inches and the second externaldiameter ED2 can be about 0.1.57 inches. A taper angle B can be definedbetween the longitudinal axis 82 of the locking fastener 32 and theexternally threaded surface 70 of the threaded head 34. Although anysuitable taper angle B can be used, suitable taper angles A can bebetween about 2 degrees and about 20 degrees, and more particularlybetween about 5 degrees and about 15 degrees, such as about 10 degrees.

As previously described, the threaded aperture 26 of the bone plate 12and the locking fastener 32 can define a “polyaxial.” fastening systemwherein the locking fastener 32 can be inserted into the threadedaperture 26 in a plurality of different insertion angles relative to thelongitudinal axis 40 of the aperture while achieving a lockingengagement between the threaded head 34 and the threaded aperture 26.The ability of the locking fastener 32 to be received within thethreaded aperture 26 at a plurality of different insertion angles canresult from, at least in part, the “mismatch” in taper angles betweenthe internally threaded aperture 26 and the externally threaded head 34of the locking fastener 32. More particularly, the taper angle B of thethreaded head 34 can be configured such that it is smaller than thetaper angle A of the threaded aperture 26, thereby allowing insertion ofthe locking fastener 32 in a range of insertion angles. Furthermore, thelarger taper angle A in the bone plate 12 can create more congruencebetween the internally threaded aperture 26 and the externally threadedhead 34 of the locking fastener 32 as the insertion angles of thelocking fastener 32 become larger. This can be important because thelocking strength is typically reduced as the insertion angle of alocking fastener is increased.

The particular range of insertion angles can depend on, for example, themagnitude of the mismatch in taper angles between the threaded aperture26 and the threaded head 34. In various examples, the range of insertionangles (relative to the longitudinal axis 40 of the threaded aperture26) can be between 0 degrees and about 30 degrees, such as between 0degrees and about 15 degrees.

The externally threaded surface 70 can include V-shaped threads defininga series of roots 100 and crests 102 and having an internal thread angleT2. Similar to the thread angle T1 of the threaded aperture 26, thethread angle T2 can be selected such that it is consistent withcommercially available tooling, such as 60 degrees (UN threads) or 29degrees (ACME threads), although various other non-standard threadangles can be used. In the present example of the locking fastener 32,the thread angle T2 of the threaded head 34 can be substantially equalto the thread angle T1 of the threaded aperture 26, or about 60 degrees.A thread height H2 of the threads of the externally threaded surface 70can be defined between one of the roots 100 and an adjacent one of thecrests 102. As illustrated in FIG. 8, the roots 100 and/or the crests102 can once again be truncated to avoid the formation of a “sharp”V-shape. In an example, the thread height H2 can be between about 0.009inches and about 0.020 inches, such as about 0.0137 inches.

FIGS. 9 and 10 are cross-sectional views of a portion of the bone platesystem 10 illustrating the polyaxial locking capability of the lockingfastener 32 and the threaded aperture 26 of the bone plate 12. Inparticular, FIG. 9 depicts the locking fastener 32 at an insertion angleof 0 degrees, wherein the longitudinal axis 82 of the locking fastener32 is aligned with the longitudinal axis 40 of the threaded aperture 26.In the straight on-axis insertion shown in FIG. 9, at least a portion ofthe externally threaded surface 70 of the threaded head 34 can engage atleast a portion of the internally threaded surface 46 of the threadedaperture 26 such that the threads are aligned an no cross-threadingoccurs. During on-axis insertion of the locking fastener 32, there canbe continuous contact between the externally threaded surface 70 of thelocking fastener 32 and the internally threaded surface 46 of thethreaded aperture 26. The counterbore 52 in the first surface 22 of thebone plate 12 can be configured to receive a thread portion of theexternally threaded surface 70 after insertion through the threadedaperture 26.

FIG. 10 depicts the locking fastener 32 inserted at an off-axis,non-zero insertion angle relative to the longitudinal axis 40 of thethreaded aperture 26. In particular, the longitudinal axis 82 of thelocking fastener 32 can define an insertion angle C with thelongitudinal axis 40 of the threaded aperture 26. As discussed above,the particular range of insertion angles C can depend on factors suchas, for example, the magnitude of the mismatch in taper angles betweenthe threaded aperture 26 and the threaded head 34. In various examples,the range of insertion angles C can be between 0 degrees and about 30degrees, such as between 0 degrees and about 15 degrees as depicted inFIGS. 9 and 10.

When the locking fastener 32 is inserted into the threaded aperture 26at an off-axis, non-zero insertion angle C, the threaded tabs 80 definedby the recesses 78 in the threaded head 34 (see FIG. 6) can deform toseat into the threaded surface 46 of the aperture 26. This deformationof the threaded tabs 80 can couple with hoop stresses caused by theoff-axis insertion to create a lock between the threaded head 34 and thethreaded aperture 26. In view of the foregoing, by providing a largertaper angle in the threaded aperture 26 of the bone plate 12 than on thethreaded head 34 of the locking fastener 32, and by further providing aplurality of threaded tabs 80 on the threaded head 34, the lockingfastener 32 can be inserted into the threaded aperture at a plurality ofdifferent off-axis insertion angles while maintaining congruence betweenthe internally threaded surface 46 of the threaded aperture 26 and theexternally threaded surface 70 of the threaded head 34, even at largeoff-axis angles of 15 degrees or more.

Unlike the on-axis insertion illustrated in FIG. 9, when the lockingfastener 32 is inserted off-axis as illustrated in FIG. 10, a portion ofthe externally threaded surface 70 of the threaded head 34 that isdisposed within the threaded aperture 26 may not actually engage theinternally threaded surface 46 of the aperture 26. Even though there maynot be continuous contact between the externally threaded surface 70 ofthe locking fastener 32 and the internally threaded surface 46 of thethreaded aperture 26, the off-axis threaded engagement can stillmaintain a locked coupling engagement between the components.

The bone plate 12 and the locking fastener 32 can be formed from anysuitable medical-grade material. Exemplary materials can include, butare not limited to, stainless steel, titanium, and cobalt based alloys.The bone plate 12 and the locking fastener 32 can be formed from thesame material or at least partially from different materials. One orboth of the locking fastener 32 and the bone plate 12 can be anodized orhard-coated to reduce insertion torque of the locking fastener 32 intothe threaded aperture 26. An example of a suitable coating can beTitanium Nitride (TiN).

The materials and coatings for the bone plate 12 and the lockingfastener 32 can be mismatched to facilitate selective deformation of onecomponent relative to the other. In an example, the threaded head 34 ofthe locking fastener 32 can be formed from a material and/or include acoating that is softer than the bone plate 12 to allow deformation ofthe threaded head 34 during insertion. Such a design can allow a firstlocking fastener to be removed and replaced with a second lockingfastener without any damage to the threaded aperture in the bone plate.

The above Detailed Description includes references to the accompanyingdrawings, which form a part of the detailed description. The drawingsshow, by way of illustration, specific embodiments in which theinvention can be practiced. These embodiments are also referred toherein as “examples.” Such examples can include elements in addition tothose shown or described. However, the present inventors alsocontemplate examples in which only those elements shown or described areprovided. Moreover, the present inventors also contemplate examplesusing any combination or permutation of those elements shown ordescribed (or one or more aspects thereof), either with respect to aparticular example (or one or more aspects thereof), or with respect toother examples (or one or more aspects thereof) shown or describedherein.

In the event of inconsistent usages between this document and anydocuments so incorporated by reference, the usage in this documentcontrols.

In this document, the terms “a” or “an” are used, as is common in patentdocuments, to include one or more than one, independent of any otherinstances or usages of “at least one” or “one or more.” In thisdocument, the term “or” is used to refer to a nonexclusive or, such that“A or B” includes “A but not B,” “B but not A,” and “A and B,” unlessotherwise indicated. In this document, the terms “including” and “inwhich” are used as the plain-English equivalents of the respective terms“comprising” and “wherein.” Also, in the following claims, the terms“including” and “comprising” are open-ended, that is, a system, device,article, composition, formulation, or process that includes elements inaddition to those listed after such a term in a claim are still deemedto fall within the scope of that claim. Moreover, in the followingclaims, the terms “first,” “second,” and “third,” etc. are used merelyas labels, and are not intended to impose numerical requirements ontheir objects.

The above description is intended to be illustrative, and notrestrictive. For example, the above-described examples (or one or moreaspects thereof) may be used in combination with each other. Otherembodiments can be used, such as by one of ordinary skill in the artupon reviewing the above description. The Abstract is provided to complywith 37 C.F.R. §1.72(b), to allow the reader to quickly ascertain thenature of the technical disclosure. It is submitted with theunderstanding that it will not be used to interpret or limit the scopeor meaning of the claims. Also, in the above Detailed Description,various features may be grouped together to streamline the disclosure.This should not be interpreted as intending that an unclaimed disclosedfeature is essential to any claim. Rather, inventive subject matter maylie in less than all features of a particular disclosed embodiment.Thus, the following claims are hereby incorporated into the DetailedDescription as examples or embodiments, with each claim standing on itsown as a separate embodiment, and it is contemplated that suchembodiments can be combined with each other in various combinations orpermutations. The scope of the invention should be determined withreference to the appended claims, along with the full scope ofequivalents to which such claims are entitled.

What is claimed is:
 1. A bone plate system, comprising: a bone plateincluding a first surface and a second surface, the bone plate includingat least one threaded aperture, the threaded aperture being conicallytapered between the first surface and the second surface at a firsttaper angle; and at least one fastener including an elongate shaft and athreaded head, the threaded head being conically tapered between aproximal end of the threaded head and a distal end of the threaded headat a second taper angle different from the first taper angle, wherein aplurality of circumferentially spaced recesses are formed in thethreaded head and define a plurality of threaded tabs; wherein the firsttaper angle is formed between a longitudinal axis of the threadedaperture and an entirely threaded surface of the threaded aperture, theentirely threaded surface being conically tapered; and wherein the atleast one fastener is configured for insertion within the at least onethreaded aperture at a plurality of different insertion angles whileachieving a locking engagement between the threaded head and thethreaded aperture.
 2. The bone plate system of claim 1, wherein thesecond taper angle is formed between a longitudinal axis of the threadedhead and an externally threaded surface of the threaded head, the firsttaper angle being greater than the second taper angle.
 3. The bone platesystem of claim 2, wherein the first taper angle is between 10 degreesand 20 degrees, and wherein the second taper angle is between 5 degreesand 15 degrees.
 4. The bone plate system of claim 2, wherein theplurality of recesses extend from the proximal end to the distal end ofthe threaded head in a direction that is substantially parallel to thelongitudinal axis of the threaded head.
 5. The bone plate system ofclaim 2, wherein the threaded surface of the threaded aperture includesdouble lead threads.
 6. The bone plate system of claim 1, wherein thethreaded aperture includes internal threads defining a first pitch, andwherein the threaded head includes external threads defining a secondpitch.
 7. The bone plate system of claim 6, wherein the first pitch andthe second pitch are the same.
 8. The bone plate system of claim 6,wherein the first pitch and the second pitch are different.
 9. The boneplate system of claim 1, comprising three or more recesses formed in thethreaded head.
 10. The bone plate system of claim 1, wherein acircumference of the threaded head includes a threaded circumferenceportion defined by the threaded tabs and a non-threaded circumferenceportion defined by the recesses, wherein the threaded circumferenceportion is greater than the non-threaded circumference portion.
 11. Thebone plate system of claim 1, wherein the threaded head is at leastpartially formed from a first material that is softer than a secondmaterial of the bone plate such that the threaded head can deform duringinsertion within the threaded aperture of the bone plate.
 12. A boneplate system, comprising: a bone plate including a bone facing surface,an opposing outer surface, and at least one linearly tapered apertureextending through the bone plate and having a longitudinal axis and athreaded internal surface, the linearly tapered aperture defining afirst taper angle between the longitudinal axis of the linearly taperedaperture and the threaded internal surface, the outer surface furtherincluding a first counterbore centered about the longitudinal axis ofthe linearly tapered aperture, and the bone facing surface furtherincluding a second counterbore centered about the longitudinal axis ofthe linearly tapered aperture, the threaded internal surface beingcontinuously linearly tapered from the first counterbore to the secondcounterbore; and at least one fastener including an elongate shaft and alinearly tapered head having a threaded external surface and alongitudinal axis, the linearly tapered head defining a second taperangle between the longitudinal axis of the linearly tapered head and thethreaded external surface, wherein a plurality of circumferentiallyspaced recesses are formed in the linearly tapered head and defineinterruptions in the threaded external surface of the linearly taperedhead; wherein the first taper angle of the linearly tapered aperture isgreater than the second taper angle of the linearly tapered head suchthat the at least one fastener can be inserted within the at least onelinearly tapered aperture at a plurality of different insertion angles.13. The bone plate system of claim 12, wherein the first taper angle isbetween 10 degrees and 20 degrees, and wherein the second taper angle isbetween 5 degrees and 15 degrees.
 14. The bone plate system of claim 12,wherein the interruptions in the threaded external surface of thelinearly tapered head define a plurality of threaded tabs on thelinearly tapered head.
 15. The bone plate system of claim 14, wherein acircumferential surface area defined by the threaded tabs is greaterthan a circumferential surface area defined by the recesses in thelinearly tapered head.
 16. The bone plate system of claim 12, whereinthe threaded internal surface of the linearly tapered aperture includesthreads defining a first pitch and the threaded external surface of thelinearly tapered head includes threads defining a second pitch, andwherein the first pitch and the second pitch are the same.
 17. The boneplate system of claim 12, wherein the threaded internal surface of thelinearly tapered aperture includes threads defining a first pitch andthe threaded external surface of the linearly tapered head includesthreads defining a second pitch, and wherein the first pitch and thesecond pitch are different.
 18. A bone plate system, comprising: a boneplate including a first surface and a second surface, the bone plateincluding at least one threaded aperture, the threaded aperture beingconically tapered between the first surface and the second surface at afirst taper angle; and at least one fastener including an elongate shaftand a threaded head, the threaded head being conically tapered between aproximal end of the threaded head and a distal end of the threaded headat a second taper angle different from the first taper angle, wherein aplurality of circumferentially spaced recesses are formed in thethreaded head and define a plurality of threaded tabs; wherein the firsttaper angle is between 10 degrees and 20 degrees, and wherein the secondtaper angle is between 5 degrees and 15 degrees; and wherein the atleast one fastener is configured for insertion within the at least onethreaded aperture at a plurality of different insertion angles whileachieving a locking engagement between the threaded head and thethreaded aperture.
 19. The bone plate system of claim 18, wherein thethreaded aperture includes double lead threads.
 20. The bone platesystem of claim 18, wherein the threaded head is at least partiallyformed from a first material that is softer than a second material ofthe bone plate such that the threaded head can deform during insertionwithin the threaded aperture of the bone plate.